Transcript BCM and XZ Scombroidei

Brett Mommer and Xuan Zhuang
phylogenetic
tree of the
fishes
www.fao.org
Unifying features of Scombroidei
• Non-protractile mouth (a secondary loss)
• Torpedo shape streamlined for fast swimming
• Extremely active group of (mostly) oceanic
pelagic fishes found in tropical, subtropical, and
temperate marine habitats.
• All are highly predacious!
• This group makes up about 10% of marine
catches.
• Class Actinopterygii
– Order Perciformes
• Suborder Scombroidei – 6 families (in no particular order)
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Scombridae – mackarels, tunas, bonitos
*Xiphiidae – swordfish
*Istiophoridae – sailfish, marlin, spearfish
Sphyraenidae – barracudas
Gempylidae – snake mackerels
Trichiuridae – cutlassfishes
*Some believe Xiphiidae and Istiophoridae belong to a
separate suborder, Xiphioidei, the billfishes (http://www.itis.gov/)
Messy phylogeny
Pholidae
Blenniidae
Order Zeiformes
Dalziel et al. (2006) Molecular Evolution of Cytochrome c Oxidase in High-Performance Fish (Teleostei: Scombroidei). J. Mol. Evol. 62:319-331.
Scombridae
mackarels, tunas, bonitos
• 15 genus, 51 species
Katsuwonus pelamis (skipjack tuna)
Acanthocybium solandri (peto)
Scomberomorus cavalla (carite lucio)
Scomber scombrus (Atlantic mackerel)
Scombridae
–tunas
Scombridae – mackarels, tunas,
bonitos
• As tuna are often
caught great
distances from
where they are
processed, poor
quality control may
lead to spoilage
Tuna
fastest swimmers
in the ocean
(60 mph)
• Morphology: streamline shape
body, dorsal fin can be hidden
within the grooves
• pink to dark red flesh greater
quantities of myoglobin
high oxygen demand
Ram ventilation
• fishes swim in straight lines at a high rate of speed
with the mouth open.
• forces water through the mouth and over the gills
• breathe passively while swimming
• an effective way of respiration
In fish which have a
reduced or no ability to
pump water into their mouth,
keeping swimming is
required to maintain
ventilation.
Warm-blooded
Some of the larger
tuna species are
warm-blooded, such
as the bluefin tuna,
they can maintain
their blood
temperature much
higher than the
water temperature.
Regional heterothermy
• A specialized type of endothermy present in tunas, billfish, and some
sharks (convergence!).
• Oxidative “red” muscle in core of fish (cruising), surrounded by
glycolytic “white” muscle (sprinting).
• As predators, they can “maintain aerobic swimming at a speed
which the prey has begun to sprint anaerobically” (Katz, 2002).
• Advantages of endothermy w/o cost of maintaining elevated overall
metabolic rate (Helfman et. al).
Non-heterotherm
Heterotherm
Regional heterothermy
• Maintain a roughly constant thermal gradient 4-20°C above
ambient
• Heat produced from red muscle contraction improves muscle power
output.
• Also a complex circulatory anatomy to deliver O2 and prevent
conduction of heat away from red muscle.
Our old friend,
The rete!
http://animaldiversity.ummz.umich.edu/site/accounts/information/Scombridae.html
Effectiveness vs. Efficiency
Hetero
Non-Hetero
Energetically less efficient (to have increased red muscle), but more
effective in open sea where there’s nowhere for prey to hide!
Katz, Stephen L. (2002) Design of heterothermic muscle in fish. J. of Exp. Biology. 205: 2251-2266
Tuna
• associate with dolphins to avoid shark
• heavy metals can be high in larger species

High position in the food chain

Subsequent accumulation
Tuna Fishing
• important
commercial
fish
• some stocks
are at risk of
collapse due
to overfishing
Xiphiidae – swordfish
• sharp bill (sword):
• not used to spear,
• but instead may be used to slash at its
prey
• or defend against its predator
olympic octopus and swordfish fencing
Xiphiidae – swordfish
• Breaching: powerful jumping from the
ocean
• dislodge parasites ----remoras or lampreys
Xiphiidae – swordfish
• Age: can live to
be more than
25 years old
• Weigh: as
much as 1,200
pounds
• Don’t have
either scales or
teeth.
Xiphiidae – swordfish
• swim alone or in a
very loose grouping
• feed on: squid , tuna
and mackerel
• few natural predators:
large sharks &
whales
Istiophoridae
– sailfish, marlin, spearfish
• 3 genus, 11 species
www.nationalgeographic.com
sailfish
distinctive dorsal fin: like a sail
• folded down to the side when swimming
• raised when feeling threatened or excited
• during feeding, a group of sailfish use their sails
to "herd" a school of fish
Marlin
• 16 ft in length, 1500 lb in weight
“Heater organs”
• Some Scombroids (22 spp) have “heater organs” around
eyes, brain, and/or spinal cord.
• Maintain tissues 10 to 15 C° above ambient.
• Modified ocular muscle cells that don’t contract, but
Pump Ca++ in a loop, burning ATP & creating heat (many
mitochondria)
• Associated with rete mirabiles; retain heat within blood
using countercurrent-exchange.
• Greatly improves vision, ability to catch prey in cold
temps. Protects CNS from temperature fluctuations
during vertical travel.
• Different eye muscles modified as heater organs in
different groups, thought to be independently evolved.
“Heater organs”
Heater organ
Brain
Anterior
EYE
Rete
Metrio et. al. (1997) Heat-Producing Organ of the Swordfish (Xiphius gladius): A Modified Eye Muscle. J. of Morphology 234:89-96
Sphyraenidae – barracudas
•1 genus, 20 species
•Considered primitive members of Scombroidei
•Tropical and subtropical oceans, also reefs.
•Ambush predators, bursts up to 27 mph.
•Up to 6 ft in length.
Gempylidae – snake mackerels
• 23 species
• Pelagic and deepwater predators
• Elongate body, long spiny dorsal fin,
posterior finlets.
• large mouth, long teeth.
• Commercially fished
Trichiuridae – cutlassfishes
•
•
•
•
40 species, shallow coastal waters worldwide.
Lost finlets, pelvic, anal, and most of caudal fin.
Fanglike teeth, eat zoops, fish, crustaceans.
Adults feed near surface during day, migrate to bottom at
night. Juveniles do the opposite.
• Can be over 2 meters long.
Population declines of predatory
fish communities
• Estimate current level ~10% preindustrial.
• Industrialized fisheries typically reduced
community biomass by 80% within 15
years of exploitation.
• Management based on
recent data alone may be
misleading; there is no
“baseline”.
•
Myers, R.A. and B. Worm. 2005. Reply to Decline of Pacific tuna populations exaggerated? Nature. 434: E2.
Worldwide Population Declines
Tuna,
Billfishes,
Swordfish
Data from
Japanese
Pelagic
Longlining
•
Myers, R.A. and B. Worm. 2005. Reply to Decline of Pacific tuna populations exaggerated? Nature. 434: E2.
ICCAT
• The International Commission for the Conservation
of Atlantic Tunas is an inter-governmental fishery
organization responsible for the conservation of tunas
and tuna-like species in the Atlantic Ocean and its
adjacent seas.
• Set a MSY (Maximum Sustainable Yield), but many
people outraged that ICCAT continues to allow
overfishing/longlining, especially by Japan.
• Western Atlantic Bluefin Tuna currently at 3% prelonglining population; same story for other spp.
• A single bluefin sold for $172,400 at the first auction
of 2001 at Tokyo's Tsukiji Fish Market.
• Lawsuits filed to protect spawning areas and put on
endangered species list...
Review Questions
What about the biology of tuna and other scombroids makes them
vulnerable to overexploitation? Why should we worry about declining
tuna populations?
What advantage do endothermic Scombroids have over fish without
endothermy? If endothermy is so great, why not commit to it? That is,
what advantage does regional heterothermy have over complete
endothermy?
What is Ram ventilation? Which fish groups can it be found? How does
it help those fishes to get oxygen?
Why do researchers think heater organs evolved multiple times in
Scombroids? How do heater organs differ from red muscle in the way
heat is created?
Why swordfishes like to jump from the ocean?